It is well known that hydroxamic acids react with isocyanates to produce carbamoyl hydroxamates, according to the equation ##EQU1## and that the latter compounds decompose spontaneously, when heated, according to the equation ##EQU2## No suggestion has been found in the literature that the adduction reaction should be employed to make polymers containing carbamoyl hydroxamate groups or that the thermal instability of these groups could be taken advantage of in such polymers.
The utility of various hydroxamic acids and derivatives thereof as isocyanate precursors has been disclosed in a number of patents. U.S. Pat. No. 3,465,024 is directed to an improved process for preparing isocyanates by the thermal decomposition of acetyl hydroxamates and includes a discussion of several prior methods of forming isocyanates from hydroxamic acids or derivatives thereof. U.S. Pat. Nos. 3,268,542; 3,480,595; 3,507,900, 3,544,583; 3,560,492; 3,560,518; 3,813,365; 3,825,554 and 3,844,862 disclose various cyclic nitrile carbonates, sulfites and oxalates which are derivable from corresponding hydroxamic acids and which may be thermally decomposed to isocyanates utilizable in the preparation of polyurethanes. The U.S. Pat. No. 3,844,862 discloses the decomposition of cyclic nitrile carbonates in the presence of a polyol, to form foamed polyurethanes. The U.S. Pat. Nos. 3,480,595 and 3,560,492 disclose polymers containing cyclic nitrile carbonate (etc.) groups which can be reacted with polyols to form CO.sub.2 (etc.) and thermoplastic polymers containing hydroxamate groups. The latter are said to decompose on mild heating to isocyanate and polyol groups which can be readducted subsequently. Hydrolysis of the cyclic nitrile carbonate (etc.) groups in the polymers to hydroxamic acid groups is also disclosed. Despite the inclusion of these latter alternatives within the bounds of single patents, the utilization of the reactivity of isocyanate and hydroxamic acid groups with each other in the formation or modification of polymers has not been contemplated.
It is an object of the present invention to provide polymers which are stable, non-toxic and readily handled under ordinary conditions but which can be utilized as source materials for isocyanate derived polymers, such as polyurethanes, polyureas, etc.
It is also an object to provide polymers of the preceding type containing a "built in" blowing agent, namely the CO.sub.2 evolved upon decomposition of carbamoyl-hydroxamate groups.
A further object is to provide polymers which may be formed in situ or disposed as shaped solids capable of being altered to flowable or "tacky" compositions, simply by heating.
Yet another object is to provide cross-linked polymers which are controllably degradable to soluble compositions by heating.
All of the foregoing objects are attainable with polymers made up of chains which contain and/or are cross-linked by carbamoyl-hydroxamate groups.